Positioning apparatus for substrates to be processed

ABSTRACT

An apparatus is provided with a plurality of stages of mounting bases on each of which is disposed upwardly orientated, narrow tapered pins around the periphery of a semiconductor wafer, and a plurality of stages of turntables, one for each of the mounting bases, with the mounting bases being capable of moving independently of the turntables. When a wafer is transferred from a transporter arm to the tapered pins, the peripheral edge of the wafer comes into contact with the inner peripheral surfaces of the tapered pins and the wafer is centered thereby. The turntable then picks up the wafer and aligns the orientation thereof. This makes it possible to position the centers of a plurality of wafers and position the orientations thereof in a simple manner.

This application is a division of U.S. application Ser. No. 08/847,721filed Apr. 22, 1997.

The present invention relates to an apparatus for positioning asubstrate to be processed such as a semiconductor wafer and, inparticular, to a positioning apparatus for aligning a center and/or arotational position of a substrate to be processed.

BACKGROUND OF THE INVENTION

In general, when a semiconductor wafer is to be processed or inspected,the orientation of the wafer must be aligned to take account of thedirectionality of the crystal of the wafer. For that reason, a simplemethod is known of forming a linear cut-out portion called anorientation flat in the wafer, to be used when the orientation flat isaligned by rollers.

This use of rollers in this manner to position the orientation flatenables wafers to be aligned in a batch while still accommodated withina cassette, and such a mechanism is used at a heat treatment stationthat performs a heat treatment on a batch of wafers, for example, with acassette placed vertically to position the wafers. When a process suchas ion implantation or patterning is performed on wafers, however, thewafers must be accurately placed with respect to the ion implantationregion or exposure region, and thus it is necessary to center the wafersas well.

Techniques are known in the prior art as methods of positioning theorientation (the direction of the orientation flats) and the centers ofthe wafers, such as a technique disclosed in Japanese Patent ApplicationLaid-Open No. 60-85536, of aligning the orientation of a wafer by aturntable and also moving that turntable in the X and Y directions toposition the center thereof in a general manner, or a techniquedisclosed in Japanese Patent Publication No. 1-28503 of orientating awafer on a stage by rollers and then moving that stage in the X and Ydirections.

Since it is wasteful to form an orientation flat in a wafer and thus cutout a wide area thereof, a method that has recently been investigatedinvolves forming a semicircular cut-out portion called a notch insteadof a orientation flat in the peripheral edge of a wafer, and thus amechanism that uses rollers to position wafers within a cassette cannotbe applied thereto without changes.

In addition, a sealable wafer cassette has been investigated as means ofsuppressing contamination of the wafers by particles, but in such a caseit is not possible to position the wafers within the cassette. Thewafers have to be removed from the cassette for positioning, but since aplurality of wafers, such as five wafers, have to be moved at a timeinto a wafer boat at a heat treatment station that performs a heattreatment on a batch of wafers, for example, the previously describedmethod of placing wafers one-by-one on a turntable would reduce thethroughput.

The previously mentioned method that uses a turntable to center a wafernecessitates X-direction and Y-direction drive mechanisms and moreoverthe amounts of drive thereof must be accurate, so that the cost isincreased by this increase in mechanical complexity. A sealed type ofwafer cassette that is designed to suppress the contamination of wafersby particles is provided with a main cassette body, which accommodates anumber of wafers (such as 13 wafers), and a lid member for hermeticallyclosing a wafer transfer port formed in the main cassette body with anO-ring therebetween. The configuration is such that the lid member islocked by, for example, the insertion of keys into the lid member,whereby it is fixed to the main cassette body.

To reduce the contamination of the wafers by particles in this case, itis preferable to partition a cassette mounting region for placing thewafer cassette from a wafer transportation region, and keep the degreeof cleanliness of the cassette mounting region higher than that of thewafer transportation region. The cassette mounting region will bereferred to as a first environment and the wafer transportation regionwill be referred to as a second environment. In one method of increasingthe cleanliness of the first environment that can be considered, thefirst environment and the second environment are separated by apartitioning wall, the wafer cassette is attached from the firstenvironment side to an aperture formed in the partitioning wall, and thewafers within the wafer cassette are removed toward the secondenvironment side.

With the above-described configuration for attaching a wafer cassette,the various components are constructed in such a manner that a gap onthe order of approximately 2 mm is formed between the wafer cassette andthe partitioning wall at the peripheral edge portion of the aperturewhen the wafer cassette has been attached to the aperture in thepartitioning wall. Since the pressure in the second environment is setto be higher than that in the first environment, clean air always flowsinto the first environment through this gap, and thus particles areprevented from penetrating from the first environment side into thesecond environment side.

However, the air flowing through this gap forms vortices. In thevicinity of the surfaces that define the gap, such as those of thepartitioning wall and the wafer cassette, the air is extremely gentlewith a velocity close to zero. Thus the air on the first environmentside is entrained into the vortices of the air flowing from the secondenvironment, so that it flows along the above surfaces into the secondenvironment side. This causes particles to penetrate into the secondenvironment together with the air and thus, although great care has beentaken to use sealed cassettes to prevent contamination of the wafers byparticles, that intention is counteracted. In addition, if the regionused for transferring wafers into a wafer boat is made to be a nitrogenenvironment, for example, it becomes difficult to manage the oxygendensity within a processing region of an apparatus designed to preventthe growth of natural oxides.

A sealed type of wafer cassette makes it impossible to position thewafers in the cassette, thus making it necessary to position the wafersafter they have been removed from the wafer cassette. The exchange ofwafer cassettes involves attaching the lid member to the current wafercassette, removing the wafer cassette from the partitioning wall, andattaching a new wafer cassette to the aperture in the partitioning wall.The removal and attachment of the lid member and the removal andattachment of the wafer cassettes themselves are time-consumingprocesses, so that the exchange of wafer cassettes takes a long time.Therefore, since the incorporation of a system that uses a sealed typeof wafer cassette makes it necessary to add the time required forpositioning the wafers and the time required for exchanging the wafercassettes, there are demands for the investigation of techniquespreventing any deterioration in throughput.

SUMMARY OF THE INVENTION

The present invention was devised in the light of these problems in theprior art and has as an object thereof the provision of a positioningapparatus that enables simple alignment of the center and/or theorientation of a substrate to be processed, such as a wafer.

Another object of the present invention is to provide a positioningapparatus that enables alignment of the center and/or the orientation ofa plurality of substrates to be processed at a time.

A further object of the present invention is to provide a positioningapparatus that enables centering of a substrate to be processed within acassette for substrates to be processed.

A still further object of the present invention is to provide anapparatus for transporting a substrate to be processed that suppressesany decrease in the cleanliness of a region in which the substrate to beprocessed is mounted, when a sealed type of cassette for substrates tobe processed is used to transport the substrate to be processed.

A yet further object of the present invention is to provide an apparatusfor transporting a substrate to be processed which is capable ofimproving throughput when a sealed type of cassette for substrates to beprocessed is used to transport the substrate to be processed.

The present invention provides in one aspect thereof an apparatus foraligning a central position and a rotational position of a substrate tobe processed, where the substrate has a peripheral edge forming a circleand a cut-out portion for rotational position detection formed in theperipheral edge; wherein the apparatus comprises a turntable which isrotatable about a vertical rotational axis and which has an uppersurface on which a substrate to be processed is mounted; detection meansfor detecting the cut-out portion of the substrate that is mounted onand rotating with the turntable; control means for controlling an amountof rotation of the turntable in accordance with a detection signal fromthe detection means, to align the rotational position of the substrateto be processed; a horizontal base for receiving a substrate to beprocessed; and inclined guide means rising from an upper surface of thebase and provided along a circular peripheral edge of the substrate tobe processed, the guide means being mounted on the base, in such amanner that the peripheral edge of the mounted substrate to be processedcomes into contact therewith and is guided thereby; the guide meanscomprising a taper that is inclined in such a manner as to separate fromthe substrate to be processed with increasing upward distance.

The present invention provides in another aspect thereof an apparatusfor positioning a substrate to be processed, comprising support meansfor supporting a plurality of substrates to be processed at intervals ina vertical direction; and pushing means provided outside the supportmeans for pushing outer peripheral edges of substrates to be processedthat are exposed from the support means, from the outside in at leastthree locations, to position the substrates to be processed.

The present invention provides in a further aspect thereof atransporting apparatus for a substrate to be processed, comprising apartitioning wall for demarcating a first environment from a secondenvironment, and having an aperture for transfer of a substrate to beprocessed; a sealed type of cassette for substrates to be processed,comprising a main cassette body having an aperture through which asubstrate to be processed enters or exits and a lid member for closingthe aperture of the main cassette body; cassette mounting means providedwithin the first environment, for supporting the cassette in such amanner that the aperture for substrates to be processed is aligned withthe transfer aperture of the partitioning wall; sealing means forforming a seal between the peripheral edge of the transfer aperture ofthe partitioning wall and the peripheral edge of the aperture of themain cassette body, to hermetically demarcate a space within thecassette from the first environment; means for positioning a substrateto be processed, provided within the second environment; a substratetransporting mechanism provided within the second environment; a lidmember for the partitioning wall for closing the transfer aperture ofthe partitioning wall in an openable manner; first opening/closing meansfor opening or closing the partitioning wall lid member; and secondopening/closing means for opening or closing a lid member of thecassette.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a substrate transporterapparatus provided with an apparatus for positioning a substrate to beprocessed in accordance with this invention;

FIG. 2 is a cross-sectional view, mainly of the components of a wafercassette shown in FIG. 1;

FIG. 3 is a perspective view of the wafer cassette;

FIG. 4 is a perspective view of the wafer cassette, sealing member,second opening mechanism, and lid member for the wall;

FIG. 5 is a plan view used to illustrate the operation of the wafertransporter apparatus;

FIG. 6 is a sectional view through another embodiment of the presentinvention relating to a wafer cassette and wafer transporter apparatus;

FIGS. 7(a) and 7(b) are views illustrative of the operation of theapparatus of FIG. 6;

FIG. 8 is a schematic perspective view of part of a transporter stationthat comprises a positioning apparatus of an embodiment of thisinvention;

FIG. 9 is an enlarged perspective view of part of FIG. 8;

FIG. 10 is a side view of FIG. 9;

FIG. 11 is a side view of tapered pins of the positioning apparatus,shown enlarged;

FIGS. 12 and 13 are plan views of different types of wafer;

FIGS. 14(a) to 14(e) are views sequentially illustrating the state ofpositioning of a wafer;

FIG. 15 is a perspective view of a variant of the tapered guide means;

FIG. 16 is a perspective view of yet another embodiment of thepositioning apparatus; and

FIG. 17 is a plan view of the positioning apparatus of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A representative embodiment of the present invention is shown in FIG. 1and a section through a main portion thereof is shown in FIG. 2. Thisdevice is demarcated by a partitioning wall 2 to form a firstenvironment S1 that is a wafer cassette mounting region and a secondenvironment S2 that is a wafer transportation region. An aperture 21 forthe transfer of wafers, which are substrates to be processed, is formedin this partitioning wall 2 as shown in FIG. 2, and a step portion 21 ais formed around a peripheral edge portion on the first environment S1side of the aperture portion 21.

An O-ring 22 formed of a resilient material such as Teflon (tradename)is provided on a step surface of the step portion 21 a (hereinaftercalled a surface facing an attachment/removal direction), to form asealing portion. This O-ring 22 is designed to provide a seal between aperipheral edge portion of a wafer cassette 3 and the aperture 21 of thepartitioning wall 2, thus hermetically separating the first environmentS1 from a space within the wafer cassette 3. A nitrogen (N2) gas supplypassage 23 and an exhaust passage 24, are provided in such a manner asto open into an inner peripheral surface of the partitioning wall 2surrounding the aperture 21, and a N2 gas source 25 and a vacuum pump 26are connected to the other ends of the N2 gas supply passage 23 andexhaust passage 24, respectively.

The sealed wafer cassette 3, which is a cassette for substrates to beprocessed, is hermetically attached to the partitioning wall 2 on thefirst environment S1 side of the aperture 21. This wafer cassette 3 isprovided with a main cassette body 31 in which are formed multiplestages of wafer holder portions 30 in such a manner that a number ofwafers W (for example, 13 wafers), which are substrates to be processed,are supported vertically at a certain spacing thereby, and a lid member32 for hermetically sealing an aperture 33 that is a wafer transfer portof this main cassette body 31, as shown by way of example in FIG. 3.

The lid member 32 is provided in such a manner that it enters within theaperture 33 of the main cassette body 31, a protruding portion 34 thatacts as a stopper for the lid member 32 is formed around the innerperipheral surface of the main cassette body 31, and an O-ring 35 isprovided between the lid member 32 and the protruding portion 34, asshown in FIG. 2. As shown in FIG. 3, keyholes 36 a are provided in, forexample, two locations on the lid member 32 and the configuration issuch that a number of locking pins 37 (for example, four pins) areforced outward from the upper and lower edges of the lid member 32 tofix together the main cassette body 31 and the lid member 32, byinserting keys 36 that are provided in a second opening mechanism (whichwill be described later) into the keyholes 36 a and rotating the same.The peripheral edge portion of the aperture 33 of the main cassette body31 is formed as a flange portion 31 a with the outer side thereof beingcurved.

The wafer cassette 3 is mounted on a stage 41 (FIG. 2) of a cassettemounting portion 4, the wafer cassette 3 is supported by this cassettemounting portion 4 at a position aligned with the aperture 21 for thetransfer of wafers, and is attached to the aperture 21 for the transferof wafers in such a manner that the flange surface of the flange portion31 a is placed in hermetic contact with the step surface of the stepportion 21 a of the aperture portion 21 for the transfer of wafers, withthe O-ring 22 therebetween. For the sake of convenience, thepartitioning wall 2 and the cassette mounting portion 4 are drawn inFIG. 1 displaced to the left from their normal positions, but inpractice these components are positioned towards the side of a firsttransporter mechanism 8A, which will be described later.

The cassette mounting portion 4 is provided with the stage 41 on whichare formed a number of protrusions 41 a (for example, four protrusions),a stage-supporting stand 42 for supporting the stage 41, and guide rails43 provided on a base 44 in a direction in which the wafer cassette 3 isattached and removed. The stage-supporting stand 42 is configured to becapable of moving along the guide rails 43 in this attachment/removaldirection of the wafer cassette 3.

Indentations 31 b are formed in a lower surface of the wafer cassette 3to match the protrusions 41 a of the stage 41, with the configurationbeing such that the wafer cassette 3 is positioned on the stage 41 bythe engagement of the indentations 31 b with the protrusions 41 a. Apushing mechanism 45 such as an air cylinder, for pressing thestage-supporting stand 42 towards the partitioning wall 2 side, isprovided on a rearward side (opposite to the second environment S2) ofthe stage-supporting stand 42.

A lid member 51 for the partitioning wall 2, for hermetically closingthe second environment S2 side of the aperture portion 21 for thetransfer of wafers, is provided on the second environment S2 side of theaperture portion 21 of the partitioning wall 2, as shown by way ofexample in FIG. 4. This lid member 51 is formed to be of a size thatcovers the peripheral edge-portion of the aperture 21 on the secondenvironment S2 side and is configured to be opened and closed by a firstopening mechanism. This first opening mechanism is provided with anelevator base 55 for raising and lowering the lid member 51 by anelevator shaft 55 a, and a horizontal base 56 for causing the elevatorbase 55 to move horizontally.

A second opening mechanism 52 for opening and closing the lid member 32of the wafer cassette 3 is provided in combination with the lid member51, and this second opening mechanism 52 has a key manipulationmechanism 53 (see FIG. 2) that moves the keys 36 forward and backward,and rotates them. A freely extendable bellows-like sealing member 54 isfixed by suction pads to the peripheral edge portion of the aperture 21on the second environment S2 side in such a manner as to hermeticallyclose the peripheral edge portion of the wall lid member 51.

The mechanism for transporting and positioning the wafers in the secondenvironment S2 will now be described with reference to FIG. 1. Withinthe second environment S2 are provided an intermediate transfer stand 6for temporary placement of the wafers; a positioning mechanism 7 forpositioning wafers disposed on a forward upper side thereof; a waferboat WB or the like that forms part of a thermal processing stationdisposed on a rearward side of the intermediate transfer stand 6; thefirst transporter mechanism 8A for transferring wafers to and from thewafer cassette 3, the intermediate transfer stand 6, and the positioningmechanism 7; and a second transporter mechanism 8B for transferringwafers to and from the intermediate transfer stand 6 and the wafer boatWB.

The intermediate transfer stand 6 is combined with a mechanism forpositioning the centers of the wafers W and is provided with mountingrings 61 for positioning the centers of the wafers, disposed in 65stages so as to be capable of accommodating more wafers than those inone cassette (13 wafers), such as the contents of five cassettes. Eachof the mounting rings 61 is provided with a number of conical tapered.pins 62, such as ten pins, disposed symmetrically five on each sidealong positions corresponding to the periphery of the wafer W. Spacesfor the insertion of the first transporter mechanism 8A and the secondtransporter mechanism 8B are formed between pairs of the tapered pins 62at the forward and rearward sides.

The positioning mechanism 7 is provided with a plurality of fixed bases71 (such as five). Each of these fixed bases 71 is provided with aturntable 72, which supports the rear surface of a wafer W and isrotated about a vertical axis by a drive portion 73, and an opticalsensor 74 for detecting a notch or orientation flat of the wafer on theturntable 72. The positioning mechanism 7 controls the angle of rotationof the turntable 72 on the basis of a detection signal from the opticalsensor 74, to align the wafer in a predetermined orientation.

Each of the first transporter mechanism 8A and the second transportermechanism 8B is provided with, for example, five transporter arms 81that are capable of transporting a plurality of wafers, such as fivewafers, at a time or a single wafer at a time. These arms are configuredto be freely movable forward/backward, vertically, and rotatably, andthe pitch (vertical spacing) therebetween is also variable.

The operation of this embodiment will now be described. First of all, awafer cassette 3 containing wafers W is mounted on the cassette mountingportion 4 and it is pushed by the pushing mechanism 45. This presses theflange surface of the flange portion 31 a of the wafer cassette 3against the step surface of the step portion 21 a of the aperture 21 forthe transfer of wafers, with the O-ring 22 therebetween, to form ahermetic seal between the first environment S1 and the secondenvironment S2.

A pure inert gas such as N2 is then supplied from the N2 gas supplypassage 23 into the space within the aperture 21 of the partitioningwall 2 (between the lid member 51 for the wall and the wafer cassette 3)while the pressure within the aperture 21 is reduced to, for example,0.07 MPa by the vacuum pump 26 through the exhaust passage 24, toreplace the air within that space with N2. The keys 36 of the keymanipulation mechanism 53 of the second opening mechanism 52 are theninserted into the keyholes 36 a of the lid member 32 of the wafercassette 3 and rotated, whereby the locking pins 37 are released,closing the lid member 32.

Subsequently, the lid member 51 of the wall is moved backwards by thehorizontal base 56 of the first opening mechanism, then is lowered bythe elevator base 55, so that the lid member 51 for the wall is removedfrom the aperture 21, together with the lid member 32. The transporterarms 81 of the first transporter mechanism 8A are then inserted into thewafer cassette 3 to pick up and hold five wafers W from the wafercassette 3 at a time and transport them into the intermediate transferstand 6. At the intermediate transfer stand 6, each of the transporterarms 81 passes through the arm insertion space at the forward side ofone of the mounting rings 61, and mounts the wafers W thereon in such amanner that the tapered surface of the tapered pins 62 of each mountingrings 61 comes into contact with the peripheral edge of a wafer W. Sincethis causes the peripheral edge of each wafer W to be controlled by thetapered surfaces of the tapered pins 62, the center of the wafer W ispositioned.

After 13 wafers W have been transported in this manner from the wafercassette 3 to the intermediate transfer stand 6, the aperture portion 21for the transfer of wafers is closed by the lid member 51 for the wall.The empty wafer cassette 3 is then replaced by a new wafer cassette 3,but the positioning of wafers W and the transporting of the wafer boatcan be done in the second environment S2 during this replacement.

In other words, the wafers W mounted on the intermediate transfer stand6 are moved by the transporter arms 81 of the first transportermechanism 8A onto the turntables 72 of the positioning mechanism 7 inthe second environment S2, as shown in FIG. 5, and notches in the wafersW are positioned as previously described. Note that upwardly protrudingpins (not shown in the figures) project from the upper surface of eachturntable 72 of the positioning mechanism 7, and the wafers W aretransferred onto these upwardly pointing pins.

After the wafers W on the positioning mechanism 7 have been transportedby the first transporter mechanism 8A to the intermediate transfer stand6, they are transported into the wafer boat WB from the intermediatetransfer stand 6 by the transporter arms 81 of the second transportermechanism 8B. This wafer boat WB is then inserted into a heat treatmentfurnace H (see FIG. 1) that is disposed above the wafer boat WB, forexample, and a predetermined heat treatment is performed.

With this wafer transporter apparatus, the aperture 21 is closed by thelid member 51 for the wall when there is no wafer cassette 3 attached tothe aperture 21 for the transfer of wafers of the partitioning wall 2.In addition, the space between the lid member 51 for the wall and theperipheral edge of the aperture 21 is sealed by the sealing member 54,so that the not-very-clean air of the first environment S1 is preventedfrom penetrating into the second environment S2.

After the wafer cassette 3 has been attached to the aperture 21, airfrom the first environment S1 does penetrate into the gap formed betweenthe wafer cassette 3 in the aperture portion 21 and the lid member 51for the wall, but this air is replaced with N2 by evacuating this gapwhile supplying N2 thereto, so that particles brought into this gap bythe air are also removed through the exhaust passage 24.

For that reason, any decrease in the degree of cleanliness within thesecond environment S2 is suppressed because the first environment S1 ishermetically sealed from the second environment S2 by ensuring that theenvironment is very clean in the gap while the lid member 51 for thewall is open, and by placing the O-ring 22 between the wafer cassette 3and the partitioning wall 2.

Furthermore, since a nitrogen environment is formed within the apertureportion 21 itself in this processing apparatus that creates a nitrogenenvironment within the second environment S2, there is substantially nodanger of oxygen entering the second environment S2 and the secondenvironment S2 can be made to be a predetermined nitrogen environment.Note that another inert gas such as argon, or very clean air, couldequally well be used as the pure gas instead of N2.

In addition, since all of the wafers W within the wafer cassette 3 arefirst moved to a temporary position on the intermediate transfer stand 6in the above-described wafer transporter apparatus, to create a state inwhich exchange can be performed while the wafer cassette 3 is empty, thetask of exchanging wafer cassettes 3 can be performed in parallel.Therefore, the time taken for positioning the wafers W is not the sum ofthe time required for transporting the wafers and the time required forexchanging the wafer cassettes 3; it can be reduced to the time taken toconvey the wafers from within the cassette 3 into the processingstation. With a hermetically sealed type of wafer cassette 3, exchangingthe wafer cassettes 3 takes a long time and the wafers W must bepositioned after they have been fetched out of the wafer cassette 3, sothis is an effective method from the viewpoint of the throughput in thesubsequent processing system.

In the embodiment described above, the lid member 51 for the wall andthe second opening mechanism 52 could be provided as separate componentsinstead of being integral, and the N2 gas supply passage 23 and theexhaust passage 24 need not necessarily be provided. Furthermore, theresilient material is not limited to the O-ring 22 and a configurationcould be used in which the pushing mechanism 45 is not provided. Inaddition, the configuration could be such that the positioning of thecenters and orientations of the wafers W is done by the positioningmechanism 7, not the intermediate transfer stand 6, and the intermediatetransfer stand 6 could be omitted. The positioning of both the centersand the orientations of the wafers W can be implemented by a combinationof the turntables 72 and the mounting rings 61, for example, where bothcomponents are configured to be freely and independently elevatable.

The above-described effects are obtained if the intermediate transferstand 6 is provided as in this embodiment, but this can also be appliedto a type of system in which air is prevented from penetrating from thefirst environment S1 into the second environment S2 by setting thesecond environment S2 to a greater pressure than the first environmentS1 and causing air to flow out of the second environment S2, as in theprior art.

A second embodiment of this invention will now be described withreference to FIG. 6. This embodiment is based on the observation that,when a wafer cassette 3 is pressed towards the step portion 21 a of theaperture portion 21 for the transfer of wafers and a resilient materialsuch as the O-ring 22 is used as a sealing member therebetween, theamount of crushing of the O-ring 22 is not stable and thus the positionat which each wafer cassette 3 is fixed in the attachment/removaldirection differs for each wafer cassette 3.

In other words, the position of the wafer cassette 3 is not constantwhich means that, even if wafers are accommodated within the wafercassette 3 with the centers thereof aligned, the pick-up position of thewafers W within the wafer cassette 3 will differ as seen from thetransporter arms 81 of the first transporter mechanism 8A. Therefore, ifthe stroke of the transporter arms 81 is set to be the same, the centerposition of the wafers W will deviate at the stage at which they havebeen transferred onto the transporter arms 81, making it necessary tore-position the centers. This embodiment is intended to solve thisproblem.

This embodiment differs from the previously described embodiment in thatit is provided with a detection means 9 such as a micro-digital scalefor detecting the position at which the cassette mounting portion 4 isfixed, on the forward side (the second environment S2 side) of thecassette mounting portion 4. In addition, a detection signal from thisdetection means 9 is input to a control means C of the first transportermechanism 8A, a control signal from this control means C is sent to adrive means 83 of the first transporter mechanism 8A, and the stroke ofthe transporter arms 81 is determined on the basis of this control inputsignal.

This micro-digital scale has a configuration in which a stick 92protrudes a predetermined distance from a main body 91, for example, andmovement distances of the order of 0.1 mm can be detected by measuringthe distance by which this stick 92 is pressed to protrude into the mainbody. With this embodiment, if the cassette mounting portion 4 stops atan initial position (the position at which the wafer cassette 3 ismounted thereon) that is just a small distance before it touches theO-ring 22, the tip of this stick 92 is disposed so as to come intocontact with the forward surface of the cassette mounting portion 4.Since the position of the stick 92 is known in this configuration, theposition of the cassette mounting portion 4 is also known, the detectionsignal from the micro-digital scale is transmitted to the control meansC as position information of the wafer cassette 3, and thus the strokeof the transporter arms 81, that is, their insertion distance into thewafer cassette 3, can be controlled.

If the amount of crushing of the O-ring 22 is small and thus themovement position of the wafer cassette 3 does not reach a previouslydetermined movement position F, as shown for example in FIG. 7(a), theinsertion distance of the transporter arms 81 into the wafer cassette 3is increased. Conversely, if the amount of crushing of the O-ring 22 islarge and thus the movement position of the wafer cassette 3 exceeds thepreviously determined movement position F, as shown for example in FIG.7(b), the insertion distance of the transporter arms 81 into the wafercassette 3 is reduced.

If the insertion distance of the transporter arms 81 is controlled inthis manner in accordance with the distance moved by the wafer cassette3, and thus the reception position of the wafers W is controlled, theposition of the wafers on the transporter arms 81 is always set to bethe same even if the degree of crushing of the O-ring 22 differs.Therefore, the position of the centers of the wafers W is fixed,increasing the accuracy with which the wafers W are moved by thetransporter arms 81 and making it unnecessary to position the centersanew.

Instead of the micro-digital scale used by way of example as thedetection means 9 in the above-described embodiment, other means couldbe used such as a scaling device, which could be a glass scale, providedon the rails 43 of the cassette mounting portion 4, for example, in sucha manner that the movement position of the cassette mounting portion 4is detected thereby. This invention can also be applied to an apparatusthat uses liquid crystal display substrates, as the substrates to beprocessed.

In order to reduce contamination by particles of the substrates to beprocessed as far as possible in the above-described embodiment, a sealedtype of cassette is used for the substrates to be processed, the firstenvironment wherein is placed the cassette of substrates to be processedis demarcated from the second environment wherein the substrates to beprocessed are moved, and the aperture for the attachment of the cassetteof substrates to be processed is sealed. Therefore, the purity of theenvironment in which the substrates to be processed are placed can bekept high and thus contamination of the substrates to be processed canbe prevented.

Part of a wafer transporter station that comprises the positioningapparatus of this invention is shown in FIG. 8. This transporter stationis provided with a sealed type of wafer cassette 3, a wafer transportermechanism 10, and a wafer positioning apparatus 11. The wafer cassette 3is provided with a casing 31 in which are formed multiple stages ofwafer holder grooves 30 in such a manner that a number of wafers W (forexample, 13 wafers) are supported vertically at a certain spacingthereby, and a lid member 32 for hermetically sealing an apertureportion that is a wafer transfer port of this casing 31.

The wafer transporter mechanism 10 is designed to transfer wafersbetween the wafer cassette 3 and the wafer positioning apparatus 11, butthe wafers could be transferred into means such as a wafer boat if thetransporter station is combined with a vertical heat treatmentapparatus, or into a load-lock chamber having multiple stages of wafergrooves if it is combined with a vacuum processing apparatus. This wafertransporter mechanism 10 is provided with a plurality of transporterarms 10 a that are capable of transporting a plurality of wafers at atime. These arms are configured to be freely movable forward/backward,rotatably, and vertically, and the vertical spacing between thetransporter arms 10 a is also variable.

The wafer positioning apparatus 11 is provided with elevator bases Illwhich are arrayed in a plurality of stages, such as five stages, and aremounting portions for positioning the centers of wafers. Each of theelevator bases 111 is a plate that is formed to be substantially annularbut is cut at a base end side thereof as indicated by reference number111 a in the expanded views of FIGS. 9 and 10. The upper surface of eachelevator base 111 is provided with tapered pins 112 that are inclinedguide means, at positions around the peripheral edge of the wafer W. Atotal of ten such pins could be provided, arranged symmetrically, fiveto a side.

A gap is formed between the tapered pins 112 to the right and left of atip end portion 111 b of each elevator base 111 to allow one of thetransporter arms 10 a to be inserted therebetween, and the verticalspacing between adjacent elevator bases 111 is set to correspond to thespacing of the transporter arms 10 a. The tapered pins 112 are formed ofa resin such as Teflon (tradename) and each is shaped as a circular conewith a tip angle θ of 15 degrees, for example, and a height h of 20 mm,as shown in FIG. 11. The base end side of each of the elevator bases 111is supported in common by left and right edge portions of an elevatorframe 113 of a rectangular shape that extends in the vertical direction.

The positioning apparatus 11 is provided with five turntables 115 asrotational portions that each support the rear surface of a wafer androtate horizontally. These turntables 115 are each provided on an upperportion of a fixed base 116 corresponding to each of the elevator bases111. Each fixed base 116 is disposed slightly lower than thecorresponding elevator base 111, for example, and the base end side ofthe fixed base 116 passes through a space surrounded by the elevatorframe 113 and is fixed in common to a fixed plate 117 that is positionedon a rear surface side of the elevator frame 113.

Each fixed base 116 is provided with a drive means 119 comprising adrive pulley 118 and a motor M, for example. Each of the turntables 115is configured so as to be capable of rotating about a verticalrotational shaft that is positioned at the center of a circular regionsurrounded by the tapered pins 112, driven by a transmission mechanismsuch as a belt 120, for example, strung from the drive pulley 118. Inthis example, each turntable 115 is positioned higher than thecorresponding elevator base 111.

The elevator frame 113 is configured in such a manner that it can beraised and lowered by an elevator mechanism 123 (see FIG. 8) alongvertical guides 122 provided on the front surface side of the fixedplate 117.

Each of the fixed bases 116 is provided with a detector portion, such asan optical sensor 125 having a light-receiving portion and alight-emitting portion, for detecting a notch 100 (see FIG. 12) or aorientation flat 200 (see FIG. 13) formed as a cut-out portion forpositioning in the circular peripheral edge of a wafer W. This opticalsensor 125 is disposed in such a manner that, when a wafer W is mountedon the turntable 115, a peripheral edge portion of the wafer W issandwiched between the light-emitting portion and the light-receivingportion in the vertical direction.

A light-receiving output of the optical sensor 125 is input to a controlunit 127. This control unit 127 has the function of controlling theamount of rotation (the angle of rotation) of the turntable by the drivemeans 119, in such a manner that the notch 100 (or the orientation flat200) of the wafer W is orientated in a predetermined direction, on thebasis of the light-receiving output.

The operation of this embodiment will now be described. It is assumedthat a sealed cassette 3 has just been mounted on a cassette stage (notshown in the figures) of a wafer transporter station. The space foraccommodating wafers within the cassette 3 is ordinarily hermeticallyshielded from the exterior by the lid member 32, in a similar manner tothat shown in FIG. 2, but the lid member 32 is opened by the lid openingmechanism (not shown in the figure) for wafer transfer. The transporterarms 10 a of the wafer transporter mechanism 10 are inserted into thecassette to pick up and hold five wafers W at a time from the cassette 3and transport them into the wafer positioning apparatus 11.

The spacing between the transporter arms 10 a in the vertical directionis 10 mm, for example, when they are taking the wafers from thecassette, but it expands to 30 mm, for example, to correspond to thespacing of the elevator bases 111 when they are transferring them to thewafer positioning apparatus 11. Each of the transporter arms 10 a isinserted up to a position that is, for example, 5 mm above thecorresponding turntable 115, as shown in FIG. 14(a). At this point, theelevator base 111 is placed at a level of a height that positions thetapered surfaces of the tapered pins 112 below the peripheral edge ofthe wafer W, the elevator base 111 is raised by the rising of theelevator frame 113 so that the peripheral edge of the wafer W issupported by the tapered surfaces of the tapered pins 112 as shown inFIG. 14(b), then it is raised even further from this holding position.This lifts the wafer W off the transporter arm 10 a, then thetransporter arm 10 a withdraws from the positioning apparatus 11.

The center of the wafer W is positioned by the support thereof by thetapered pins 112. In other words, the peripheral edge of the wafer W isregulated by the tapered surfaces of the tapered pins 112, so that if,for example, the center of the wafer W is displaced, the part of theperipheral edge thereof that is on the side to which the center isoffset will come into contact with the tapered surface of a tapered pin112 first, and the rising of that tapered surface will push theperipheral edge back in the horizontal direction. Since locations at thesame height on the tapered surfaces of the ten tapered pins 112 aredisposed at positions around a circle corresponding to the outer shapeof the wafer W, the center position of the wafer is aligned when thewafer W is supported by all of the tapered pins 112 as shown in FIG.14(b).

The elevator bases 111 are then lowered and the wafers W on the elevatorbases 111 are transferred to the turntables 115, as shown in FIG. 14(c).Each of the turntables 115 is rotated by the drive means 119. Since theoptical axis of the optical sensor 125 is set so that it passes throughthe cut-out portion of the wafer W, such as the notch 100, the notch 100of the wafer W can be detected by the control unit 127 on the basis ofthe detection signal from the optical sensor 125, and the turntable 115is rotated until the orientation of the wafer W reaches a predeterminedposition.

After the positioning of the center and orientation of each wafer W hasbeen completed, the elevator bases 111 are raised to transfer the wafersW onto the turntables 115, as shown in FIG. 14(d). The transporter arms10 a are then inserted again between the wafers W and the turntables115, and the transporter arms 10 a are raised to transfer the wafers Wfrom the elevator bases 111, as shown in FIG. 14(e), and transport theminto a wafer boat of, for example, a vertical heat treatment apparatus.

In accordance with the above embodiment, throughput is improved becausecentering and orientation alignment can be performed for a plurality ofwafers W at a time, which is effective for coping with the throughputproblem when a sealed type of cassette 3 or the like is used. Since thecenters of the wafers W are positioned by the tapered pins 112, then thewafers W are transferred from the tapered pins 112 to the turntables 115and the orientations thereof are aligned, the configuration is simple.Furthermore, since the mechanism for positioning individual wafers isprovided with several stages, a compact dedicated space will sufficetherefor.

With the present invention, the configuration could be such that thebases 111 are fixed but the turntables 115 are raised and lowered, andthe transporter arms 10 a are raised and lowered when the wafers aretransferred from the transporter arms 10 a to the bases 111. However, insuch a case, the transporter arms 10 a are positioned above the taperedpins 112 in anticipation of the greatest deviation of the centerpositions of the wafers, and the wafers W are raised up from below, sothat the vertical distance through which the wafers W move will increaseand the size of the optical sensor 125 must be increasedcorrespondingly. In contrast, if the bases 111 are raised and lowered,the level of the height of each wafer W is fixed until the wafers W aretransferred from the transporter arms 10 a to the bases 111, so that thevertical distance through which the wafers W move is small and thereforethe optical sensor 125 can be made smaller in the vertical direction.

Instead of the tapered pins 112 described above, the inclined guidemeans could be configured as a protruding portion 112A extending aroundthe periphery, with the inner peripheral side thereof formed as an innertapered surface that is inclined in such a manner that it separates fromthe wafer with increasing height, as shown in FIG. 15, so that theentire peripheral edge of the wafer (except for locations correspondingto insertion spaces for the transporter arm, etc.) is supported thereby.Furthermore, the positioning mechanism of this invention, comprisingcomponents such as the bases 111 and turntables 115, could equally wellbe provided as a single stage instead of a number of stages.

A further embodiment of the present invention will now be described withreference to FIGS. 16 and 17. This embodiment concerns an apparatus forpositioning wafer centers while the wafers are accommodated within awafer cassette. A standard cassette tested under the rules of, forexample, the Semiconductor Equipment and Materials Institute (SEMI) isused as the cassette. In these figures, reference number 130 denotes awafer cassette that is placed in a lateral orientation on a cassettemounting stand 131, which is a cassette mounting portion, so that wafersW are arranged substantially horizontally. In this lateral orientationof the wafer cassette 130, an upper surface plate 132 and a lowersurface plate 133 are formed to be substantially circular and slightlylarger than the outer edge of the wafers W, and front edges 132 a and133 a of these plates 132 and 133 are formed to a circular arc shape ofclose to the same radius as that of the outer edge of the wafers W. Sidewalls 135 and 136 are formed along the peripheral edges of the plates132 and 133 between the plates 132 and 133 and on the left and rightsides thereof, a wall portion 137 is also formed at a rear portionbetween the plates 132 and 133, and 13 support grooves 138 are formed onthe inner peripheral surfaces of these wall portions 135, 136, and 137to support each of the peripheral edges of 13 wafers.

The space between the arc-shaped front edges 132 a and 133 a of theseplates 132 and 133 is formed as an aperture 140 that acts as a port forremoving and inserting wafers W. Similarly, portions are cut out of theleft and right sides at the rear of the walls 135 and 136 to formapertures 140 between the plates 132 and 133 (see FIG. 17). Theapertures 140 are not really visible in FIG. 17.

Pushing mechanisms 150A and 150B are provided symmetrically on the leftand right sides of the cassette 130 for pressing against the peripheraledge portions of the wafers in the cassette 130. The positioningmechanism of this embodiment of the invention is configured of thesepushing mechanisms 150A and 150B. The pushing mechanisms 150A and 150Bhave the same construction. Pushing members, such as rotatable rollers142 rotating about vertical shafts 141 are provided at positionsopposite to the peripheral edge portions of the wafers W where they areexposed in the vicinity of the left and right side edges of the aperture140 of the cassette 130, that is, at positions opposite to regionsfacing the front edge surfaces of the walls 135 and 136.

Each of the rollers 142 is divided into sections for each wafer W,corresponding to the wafers W within the cassette, so that the samenumber of roller elements 142 a as the number of wafers W in thecassette, such as 13, are arrayed in the heightwise direction tocorrespond to the heightwise positions of the wafers W. Spacer membersthat cannot be seen in the figures are threaded onto each shaft 141between the roller members 142 a, to maintain the spacing between theroller members, so that the roller members 142 a can rotateindependently without rubbing against each other.

Rollers 145 that are similar to the rollers 142 and are free to rotateabout vertical shafts 144 are also provided at positions opposite to theapertures 141 formed to the left and right of the rear side of thecassette 130. Lower end portions of the shafts 141 and 144 of theserollers 142 and 145 are fixed to common sliding plates 148. The upperends of these shafts 141 and 144 are connected together by linkingmembers 147.

The sliding plates 148 are configured to be free to move forwards andbackwards in a direction perpendicular to a center line L linking thefront and rear of the cassette 130 (so that they move to the left andright in FIG. 16), while being guided along guide rails 150 and 151. Adrive portion such as an air cylinder 152 is provided on a side portionof each sliding plate 148 for moving that sliding plate 148 forwards andbackwards. The four rollers 142 and 145 of the pressuring mechanisms150A and 150B are positioned in such a manner that they are in contactwith the peripheral edges of the wafers W when the centers of the wafersW in the cassette 130 are aligned. A material such as Teflon (tradename)is used for the rollers 142 and 145.

With the above-described embodiment, a cassette 130 containing 13 wafersW, for example, is placed laterally on the cassette mounting stand 131of a cassette entrance/exit port of a vertical heat treatment apparatusor the like. At this point, the rollers 142 and 145 of the transportermechanism are moved back to positions where they do not impede thecassette 130. After the cassette 130 has been placed on the mountingstand 131, the sliding plates 148 are moved forwards by the aircylinders 152 to press the rollers towards the direction of thecenterline L at four locations on the peripheral edge portions of thewafers exposed from the apertures 140 and 141 of the cassette 130,whereby the centers of all of the wafers W within the cassette 130 aresimultaneously positioned. The rollers 142 and 145 then move back andconveyor arms (not shown in the figures) start removing the wafers Wwithin the cassette 130.

This pair of pushing mechanisms 150A and 150B are disposed facingtowards the left and right in FIG. 17, but the same positioning effectcould be obtained by a pair of pushing mechanisms 150C and 150D disposedat the top and bottom of the paper in FIG. 17.

In the embodiment described above, the center positioning can beperformed for all of the wafers W within the cassette 130, thus makingit possible to improve the throughput. This embodiment is effectivebecause the previously mentioned standard cassette is fabricated todimensions with tolerances concerning wafer size and thus thepermissible positioning accuracy of the centers of the wafers is onlythe order of within a circular region of diameter 4 mm. For processingin which the orientation of the wafers is not too critical, the waferswithin the cassette can be transferred as they are into the processingstation. Alternatively, if accurate alignment of the wafer orientationis required, alignment of the wafer orientation alone can be performedsubsequently, so that a simple mechanism will suffice for thepositioning.

Note that the members that press against the peripheral edges of thewafers are not limited to rollers, but the use of rollers makes itpossible to suppress the generation of particles due to friction becausethe rollers rotate when tangential forces are applied thereto during thepushing. In addition, a single roller could be used in common for all ofthe wafers, but the use of rollers that are separated for each of thewafers means that they can rotate independently in answer to anydeviation in the central position of individual wafers, enabling afurther suppression of friction between the rollers and the wafer edges.

It should be noted that the type of cassette is not limited to thestandard cassette shown in FIG. 7. Similarly, the pressuring of thewafer edges could be done at three or more locations; it is not limitedto four locations.

The above description concerned the positioning of wafers accommodatedwithin a cassette, but the principles described herein can also be usedfor centering a wafer that is mounted on a notch aligner device.

Since the present invention combines a rotational mounting portion witha mounting portion that is provided with a tapered portion and is usedto center a wafer, it enables positioning of the center and orientationof a wafer by a simple configuration. It is also possible to position aplurality of wafers a time, by providing a plurality of stages of thepositioning mechanism formed of these mounting portions. Since theapparatus is configured in such a manner that the peripheral edges ofwafers exposed from a wafer cassette are pushed in at least threelocations, centering can be performed on wafers within the wafercassette.

What is claimed is:
 1. An apparatus for positioning substrates to beprocessed, comprising: a substrate cassette for horizontally supportingtherein a plurality of substrates at intervals in a vertical directionwithout regard for whether the center of each substrate is aligned withthe center of any other substrate, said substrate cassette having sidewalls defining a plurality of side apertures in a shape which allowsouter peripheral edges of the substrates supported in said cassette tobe exposed outside the cassette; and pushing mechanisms disposed outsidesaid substrate cassette and provided to move toward and away from saidside apertures, each of said pushing mechanisms having a pair ofvertically and parallelly extending rotatable rollers having a verticallength engageable with the exposed outer peripheral edges of all of thesubstrates in the cassette to press and position the substrates wherebythe center of each substrate comes into alignment with the center ofeach other substrate in said cassette to define a common vertical axisthrough the substrates when the pushing mechanism moves to one of saidapertures, wherein said pushing mechanisms are provided on oppositesides of the substrate cassette, respectively, to move toward and awayfrom each other.
 2. The apparatus as defined in claim 1, wherein saidsubstrate cassette has an upper surface plate and a lower surface plate.3. The apparatus as defined in claim 1, wherein each of said rotatablerollers is formed of a plurality of independently rotatable rollerelements.
 4. The apparatus as defined in claim 1, wherein each of saidpushing mechanisms is movable on and along guide rails.
 5. The apparatusas defined in claim 1, wherein said rotatable rollers are supported on acommon plate movable on and along guide rails, said rotatable rollersbeing connected to each other at upper ends thereof through a linkingmember.